diff options
| author | Ian Rogers <irogers@google.com> | 2025-10-16 13:51:24 -0700 |
|---|---|---|
| committer | Thomas Gleixner <tglx@kernel.org> | 2026-01-14 08:56:41 +0100 |
| commit | a339671db64b12bb02492557d2b0658811286277 (patch) | |
| tree | 574f8370f2eb90a5a92c0aad5d8d96d2f37fb407 /include | |
| parent | df0f9a664be55a8529362a1ada847a19a91e4807 (diff) | |
vdso: Switch get/put_unaligned() from packed struct to memcpy()
Type punning is necessary for get/put_unaligned() but the use of a packed
struct violates strict aliasing rules, requiring -fno-strict-aliasing to be
passed to the C compiler.
Switch to using memcpy() so that -fno-strict-aliasing isn't necessary.
Signed-off-by: Ian Rogers <irogers@google.com>
Signed-off-by: Thomas Gleixner <tglx@kernel.org>
Link: https://patch.msgid.link/20251016205126.2882625-3-irogers@google.com
Diffstat (limited to 'include')
| -rw-r--r-- | include/vdso/unaligned.h | 41 |
1 files changed, 35 insertions, 6 deletions
diff --git a/include/vdso/unaligned.h b/include/vdso/unaligned.h index ff0c06b6513e..9076483c9fbb 100644 --- a/include/vdso/unaligned.h +++ b/include/vdso/unaligned.h @@ -2,14 +2,43 @@ #ifndef __VDSO_UNALIGNED_H #define __VDSO_UNALIGNED_H -#define __get_unaligned_t(type, ptr) ({ \ - const struct { type x; } __packed * __get_pptr = (typeof(__get_pptr))(ptr); \ - __get_pptr->x; \ +#include <linux/compiler_types.h> + +/** + * __get_unaligned_t - read an unaligned value from memory. + * @type: the type to load from the pointer. + * @ptr: the pointer to load from. + * + * Use memcpy to affect an unaligned type sized load avoiding undefined behavior + * from approaches like type punning that require -fno-strict-aliasing in order + * to be correct. As type may be const, use __unqual_scalar_typeof to map to a + * non-const type - you can't memcpy into a const type. The + * __get_unaligned_ctrl_type gives __unqual_scalar_typeof its required + * expression rather than type, a pointer is used to avoid warnings about mixing + * the use of 0 and NULL. The void* cast silences ubsan warnings. + */ +#define __get_unaligned_t(type, ptr) ({ \ + type *__get_unaligned_ctrl_type __always_unused = NULL; \ + __unqual_scalar_typeof(*__get_unaligned_ctrl_type) __get_unaligned_val; \ + __builtin_memcpy(&__get_unaligned_val, (void *)(ptr), \ + sizeof(__get_unaligned_val)); \ + __get_unaligned_val; \ }) -#define __put_unaligned_t(type, val, ptr) do { \ - struct { type x; } __packed * __put_pptr = (typeof(__put_pptr))(ptr); \ - __put_pptr->x = (val); \ +/** + * __put_unaligned_t - write an unaligned value to memory. + * @type: the type of the value to store. + * @val: the value to store. + * @ptr: the pointer to store to. + * + * Use memcpy to affect an unaligned type sized store avoiding undefined + * behavior from approaches like type punning that require -fno-strict-aliasing + * in order to be correct. The void* cast silences ubsan warnings. + */ +#define __put_unaligned_t(type, val, ptr) do { \ + type __put_unaligned_val = (val); \ + __builtin_memcpy((void *)(ptr), &__put_unaligned_val, \ + sizeof(__put_unaligned_val)); \ } while (0) #endif /* __VDSO_UNALIGNED_H */ |